Very Computer

AIX trace does not let me see the arguments to system calls, but
I must assume that they call select with timeout pointing to a zero-
valued timeval, to affect a poll of the incoming TCP connections.

Sybase states that they do this as a performance improvement.  Are
they really going to get better response by polling each TCP socket
individually rather than using SIGIO?

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"The mere act of drinking beer in an attempt to measure your tolerance
 is likely to affect your impression of how many beers you've drunk."
        -- The Heineken uncertainty principle.

If they are saying that they use select to poll and not to actually wait
for some interval and that makes the performance better, then there must
be something flaky about AIX.  Perhaps they are using the polling to keep
the process (or at least tiny parts of it) from being paged out.  Even that
doesn't make sense as AIX has the plock call.

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Apertus Technologies, Inc.
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: AIX trace does not let me see the arguments to system calls, but
: I must assume that they call select with timeout pointing to a zero-
: valued timeval, to affect a poll of the incoming TCP connections.

: Sybase states that they do this as a performance improvement.  Are
: they really going to get better response by polling each TCP socket
: individually rather than using SIGIO?

Yes and no. Yes, polling with select() on multiple sockets is
more efficient than waiting for SIGIO. No, the above scenario
doesn't make sense. If select was called with a zero timeval,
during idle periods select() should poll (wait) until there
is activity. It should not keep calling select() over and
over again when there is no activity!

-Ade Barkah

Quote:> Sybase SQL servers running on our AIX machines use up rediculous amounts
> of CPU even when completely idle.  Running a trace of the system
> indicates that they are calling select() over and over and over.

> AIX trace does not let me see the arguments to system calls, but
> I must assume that they call select with timeout pointing to a zero-
> valued timeval, to affect a poll of the incoming TCP connections.

> Sybase states that they do this as a performance improvement.  Are
> they really going to get better response by polling each TCP socket
> individually rather than using SIGIO?

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Brahmsstr. 3                    Tel.: +49 511 660238

--
     + ------------------------+
     | David Spencer           |

     + ------------------------+

  The reason they are not doing a blocking select is that they need to
  be doing real work in the meantime.  The whole database server is
  a single Unix process, so it needs to do database-type things when not
  servicing socket I/O.

--

The Northern Trust Company              Voice:  +1 312 630-0735
Chicago, IL  60675                      FAX:    +1 312 630-6797

"The mere act of drinking beer in an attempt to measure your tolerance
 is likely to affect your impression of how many beers you've drunk."
        -- The Heineken uncertainty principle.